(1) Field of the Invention
The present invention relates to a printing plate which can be made by the electrophotographic process. More particularly, the present invention relates to a novel printing plate comprising a negatively charged electrophotographic photosensitive material having a sensitivity to a white light, gas laser or light-emitting diode as the light source, which is made by forming a toner image through a series of steps of the electrophotographic process and eluting the photosensitive layer of a non-image area.
(2) Description of the Related Art
A positive type PS plate comprising a diazo compound and formed by utilizing photodisintegration, and a negative type PS plate comprising an acrylic prepolymer and formed by utilizing photocuring are practically used as a planographic printing plate, but since the sensitivity of these plates is low, an original is prepared by using a silver salt film and the light exposure is carried out while the original is closely adhered to the plate material. Accordingly, the plate-making process is complicated and completion of the plate-making process takes a long time, and these printing plates are unsatisfactory in that the manufacturing cost is too high.
A known zinc oxide/resin dispersion type printing plate (zinc oxide master paper) is a high-sensitivity printing plate formed by utilizing the electrophotographic process. In this technique, a planographic printing plate is made by irradiating an original with light, exposing a plate-forming material to reflected light obtained by the irradiation, to form an electrostatic latent image, and reproducing the latent image by a developing agent. Furthermore, if an aqueous solution comprising a ferrocyanide or phytic acid as the main component (so-called etching solution) is used for the surface treatment, to render the non-image area hydrophilic, a planographic printing becomes possible. This process is called a direct plate-making process and is advantageous in that, since the plate-making process is simple, the plate-making time can be shortened and the running costs are low. Nevertheless, this process is unsatisfactory in that the printing durability of the formed printing plate is lower than 10,000 prints, and that the range of printing conditions (the kinds of ink, etching solution and wetting water that can be used) is narrow. Moreover, although the zinc oxide/resin dispersion printing plate has a sensitivity to the visible rays of a halogen lamp, it does not show a practically applicable sensitivity to the long-wavelength rays of an He-Ne laser or light-emitting diode.